The invention relates to a process for the open-and closed-loop control of an internal combustion engine with a common rail system including individual accumulators.
An internal combustion engine with a common rail system together with individual accumulators and a controlling and regulating process are known from DE 103 44 181 A1. The process consists of a first step in which the individual accumulator pressure is detected and stored within a measuring interval such as one operating cycle of the internal combustion engine corresponding to a crankshaft angle of 720° . In the second step, the absolute minimum value is determined from the stored values. The absolute minimum value is equivalent to the end of the main injection. In the third step, an intermediate value is calculated on the basis of the maximum pressure value. Then, in the fourth step, a mathematical function such as a straight-line equation is used to calculate a virtual starting time for the main injection on the basis of the end of the main injection and the intermediate value. The further open- and closed-loop control of the internal combustion engine then proceeds on the basis of the virtual injection staring time, which is set as the actual starting time. There is no information to be derived from this source concerning pre-injection or post-injection in a common rail system with individual accumulators.
DE 10 2006 007 365 B3 describes a process for detecting the end of a main injection in an internal combustion engine with a common rail system including individual accumulators. In this process, the individual accumulator pressure is again determined within a measuring interval and stored. This process is based on the realization that, during the measuring interval, the change in pressure in the individual accumulator has a falling branch, i.e., injection activated, and a rising branch, i.e., injection deactivated. Thus the end of the main injection must lie at the connecting point between the rising and falling branches. In concrete terms, the process consists of a step in which, proceeding from a first pressure level of the individual accumulator pressure, a check is made to see whether two measurement values have been determined. If this is so, the process is repeated at a lower pressure-level. This recursion process is repeated until only one measurement value or no measurement value is determined. This is the case only at the end of the injection or when the end of injection occurred shortly before. A virtual start of injection is calculated on the basis of the end of the main injection in a way similar to that described in the previously mentioned DE 103 44 181 A1, and this value is taken as the actual start of injection for the further open- and closed-loop control of the internal combustion engine. No information on pre-injection or post-injection in a common rail system with individual accumulators can be found in this source either.
In the case of multiple post-injections in a common rail system with individual accumulators, the problem occurs in practice that the individual accumulator pressure has a great deal of waviness during post-injection. These oscillations of the fuel pressure in the individual accumulator are caused by the mechanical closing of the injector needle. Because the amplitudes of the desired signal, that is, the theoretical curve of the individual accumulator pressure, and the amplitudes of the superimpositions, i.e. the amplitudes of the pressure oscillations responsible for the “waviness”, are of similar magnitude, incorrect conclusions can be drawn concerning the points at which a post-injection starts and ends.